For operating vapor power cycle with excellent efficient thermal efficiency and effective heat-to-power conversion, using high-temperature heat source and low-temperature heat source having a small heat difference, a vapor power cycle has been proposed that uses as a working fluid a mixed medium of water and a fluid having a lower boiling point than water or a mixed medium of fluid materials each having a lower boiling point than water. For example, Japanese Patent laid-Open No. 7-91361 describes such a conventional vapor power cycle system.
The conventional vapor power cycle system has a configuration similar to a typical Rankine cycle for effecting vapor power cycle, and comprises an evaporator, an expander (turbine), a condenser and a compressor (pump), as well as a gas/liquid separator for separating working fluid heated in the evaporator into gas-phase working fluid and liquid-phase working fluid, an absorber which causes liquid-phase working fluid to absorb part of gas-phase working fluid after expansion at a previous stage of the condenser, a regenerator which causes to liquid-phase working fluid taken from working fluid heated in the evaporator to perform heat-exchange with low-temperature and liquid-phase working fluid before heat-exchange in the evaporator, and a heater which causes high-temperature and liquid-phase working fluid extracted from between the expander stages to perform heat-exchange with low-temperature and gas-phase working fluid.
The conventional vapor power cycle system has advantages that it can provide a higher thermal efficiency than common Rankine cycles that use a single working fluid, and particularly that the expander is extracted and the absorber causes part of gas-phase working fluid to be absorbed in liquid-phase working fluid to reduce the amount of the gas-phase working fluid heat-exchanging with the low-temperature heat source in the condenser, thereby achieving a reduced load on the condenser and an increased efficiency of the whole system and eliminating the requirement for too large-sized a condenser and the associated cost increase.